Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $114.73   10.130%   $126.3521   $126.35   $126.35   $126.40  
  Purchase #2 $94.35   9.854%   $103.6472   $103.65   $103.65   $103.60  
  Purchase #3 $146.86   12.358%   $165.009   $165.01   $165.00   $165.00  
  Purchase #4 $175.74   11.508%   $195.9642   $195.96   $195.95   $196.00  
  Purchase #5 $107.48   11.452%   $119.7886   $119.79   $119.80   $119.80  
  Purchase #6 $70.93   9.859%   $77.923   $77.92   $77.90   $77.90  
  Purchase #7 $170.55   10.137%   $187.8387   $187.84   $187.85   $187.80  
  7 purchase totals = $880.64       $976.5228   $976.52   $976.50   $976.50